In fields of forming fine patterns such as semiconductor wafers or flat panel display devices, plasma is generated and various surface treatments including dry etching, chemical vapor deposition, sputtering and the like, are performed. In recent years, to achieve a reduction in cost and improvement in throughput, wafers for semiconductor devices or substrates for flat panel display devices, tends to be larger, for example, 300 mm or greater. Accordingly, the size of a plasma generator for fabricating a large-sized wafer or substrate gradually increases. Plasma generators are classified into inductively coupled plasma generators, capacitively coupled plasma generators and the like. Also, modified plasma generators in which a magnetic field is applied to a basic plasma generator, have been known.
An inductively coupled plasma generator has a higher plasma density than a capacitive coupled plasma generator. However, the inductively coupled plasma generator requires various additional elements for improvement of uniformity. For example, a dielectric material having a thicker central portion than other portions or a dome-shaped antenna may be employed. However, this approach is complicated to carry out and is difficult to be applied to oxide etching. In other words, since oxide etching requires high selectivity in view of processing conditions, a conventional inductively coupled plasma generator in which uniformity of plasma is controlled by a diffusion method, uses a relatively bulky chamber, resulting in an increase in the residence time of gas in the chamber. Also, the conventional inductively coupled plasma generator provides a high electron temperature (Te) of plasma. As described above, there are several disadvantages in using the conventional inductively coupled plasma generator.
The inductively coupled plasma generator will now be described in detail. The inductively coupled plasma generator includes a chamber in which plasma is generated. The chamber includes a gas inlet through which a reaction gas is supplied, a vacuum pump for maintaining the inside of the chamber to be vacuum and exhausting the reaction gas after completing the reaction, and a gas outlet. Inside the chamber is provided a chuck for mounting a sample such as a wafer or a glass substrate. An antenna connected with a high-frequency power source (generally 13.56 MHz), is installed above the chamber. An insulation plate is installed between the antenna and the chamber to reduce capacitive coupling between the antenna and plasma, thereby promoting energy from the high-frequency power source to be transferred to plasma by inductive coupling.
In the inductively coupled plasma generator having the above-described configuration, a chamber is evacuated by a vacuum pump at an initial stage to make the chamber vacuum, and a reaction gas for generating plasma is then introduced into the chamber through a gas inlet so that the chamber is maintained at a predetermined pressure level. Then, high-frequency power is applied to the antenna from the high-frequency power source.
The conventional inductively coupled plasma generator has employed a single spiral antenna or a plurality of separate electrode type antennas. As RF power is applied, a magnetic field varying over time is formed in a direction perpendicular to a plane formed by the antenna. Such a magnetic field varying over time forms an inductive electric field inside the chamber, and the inductive electric field heats electrons, thereby generating plasma inductively coupled to the antenna. The heated electrons collide with neural gas particles present around the electrons and generate ions and radicals to be used in plasma etching and deposition. Also, if power is applied to a chuck from a separate high-frequency power source, it is possible to control the energy of ions incident to a sample.
However, in the spiral antenna, since the respective inductive coils constituting the antenna are connected to one another in series, a constant current amount flows through each inductive coil. In this case, it is difficult to adjust distribution of inductive electric field, causing loss in ions and electrons on the inner wall of the chamber. Thus, plasma density is unavoidably increased at the center of the chamber and reduced in the neighborhood of the inner wall of the chamber. Thus, it is quite difficult to maintain plasma density at a uniform level.
Also, since the respective inductive coils of the antenna are connected to one another in series, a voltage drop due to the antenna is increased and the antenna is greatly affected by capacitive coupling with plasma. Thus, power efficiency is lowered and it is difficult to maintain uniformity of plasma density.
Next, in the antenna constructed of three separate electrodes, plasma density is high at a location close to the respective separate electrodes connected to three different high-frequency power sources, and plasma density is low at the center of the chamber, making it difficult to maintain uniformity of plasma. In particular, it is quite difficult to process samples over a wide area. Also, since independently operating power sources are used, the cost increases. Further, for impedance matching for efficiently using power, independent impedance matching circuits must be used for the respective electrodes.
In a parallel antenna configured such that multiple circular antennas are concentrically connected to one another in parallel, uniformity of plasma in a rotating direction is lowered, that is, the plasma density is relatively high at the central portion of the antenna and is relatively low at a powered end and a ground end of the antenna. In such a manner, plasma density becomes asymmetrical with respect to the rotating direction because a relatively high voltage is applied to the powered end of the antenna, causing ion loss, resulting in a drop in plasma density. Also, since there is no current flow at a disconnected portion of a loop-type antenna, that is, between the powered end and the ground end, an inductive electric field is not generated, so that less plasma is generated thereat, resulting in a reduction in plasma density. Accordingly, uniform processing of a target material to be processed is difficult to achieve.